Gonadal steroid hormones regulate reproductive and social behaviors in many vertebrates. They do this, in part, by acting directly on the brain, particularly the hypothalamus and preoptic areas. They also influence social signals (e.g., odors) that animals produce; this, in turn, alters responses elicited from conspecifics. Finally, social behaviors and their sensitivity to hormonal control are affected by social experiences (e.g., the stress of social subordination). The proposed research attempts to determine how hormones act on the brain to modify behavior. This research involves manipulating hormonal titers by gonadectomy and hormone therapy, lesioning neural tissue, administering hormones and drugs systemically and directly into the brain, and analyzing hormone interactions with chromatin. Studies of cellular mechanisms of hormone action will emphasize estrogen control of sexual receptivity in female rats. Androgen action will be studied by comparing its effects on sexual behavior and communication (scent marking) in gerbils with its effects on both sexual behavior in male rats and scent marking in male mice. Thus we are attempting to determine how general, or how varied, the hormonal mechanisms are. Studies of social subordination will examine the social conditions that aid recovery from this stress and will explore the role of gonadal androgens in this process.